Targets and timetables - A target is the reduction of a specific percentage of heat-trapping gas (greenhouse gas)
emissions from a baseline date (e.g., below 1990 levels) to be achieved by a set date or timetable (e.g., 2030). Targets and timetables are an emissions cap on the total amount of heat-trapping gas emissions that can be emitted by a country or region in a given time period.

Tax - A carbon tax is a levy on the carbon content of fossil fuels. Because virtually all of the carbon in fossil fuels is ultimately emitted as CO2, a ► carbon tax is equivalent to an emission tax on each unit of CO2-equivalent emissions. An ► energy tax - a levy on the energy content of fuels - reduces demand for energy and so reduces CO2 emissions from fossil fuel use. An ► eco-tax is designed to influence human behavior (specifically economic behavior) to follow an ecologically benign path. An ► international carbon/emission/energy tax is a tax imposed on specified sources in participating countries by an international authority. The revenue is distributed or used as specified by this authority or by participating countries. A ► harmonized tax commits participating countries to impose a tax at a common rate on the same sources, because imposing different rates across countries would not be cost-effective. A ► tax credit is a reduction of tax in order to stimulate purchasing of or investment in a certain product, like heat-trapping gas (greenhouse gas) emission reducing technologies. A ► carbon charge is the same as a carbon tax.

Technology transfer - The exchange of knowledge, hardware and associated software, money and goods among stakeholders, which leads to the spreading of technology for adaptation or mitigation. The term encompasses both diffusion of technologies and technological cooperation across and within countries.

Teleconnection - A connection between climate variations over widely separated parts of the world. In physical terms, teleconnections are often a consequence of large-scale wave motions, whereby energy is transferred from source regions along preferred paths in the atmosphere.

Thermal expansion - In connection with sea level, this refers to the increase in volume (and decrease in density) that results from warming water. A warming of the ocean leads to an expansion of the ocean volume and hence an increase in sea level. See Sea level change.

Thermal infrared radiation - Radiation emitted by the Earth's surface, the atmosphere and the clouds. It is also known as terrestrial or longwave radiation, and is to be distinguished from the near-infrared radiation that is part of the solar spectrum. Infrared radiation, in general, has a distinctive range of wavelengths (spectrum) longer than the wavelength of the red color in the visible part of the spectrum. The spectrum of thermal infrared radiation is practically distinct from that of shortwave or solar radiation because of the difference in temperature between the Sun and the Earth-atmosphere system.

Thermocline - The layer of maximum vertical temperature gradient in the ocean, lying between the surface ocean and the abyssal ocean. In subtropical regions, its source waters are typically surface waters at higher latitudes that have subducted and moved equatorward. At high latitudes, it is sometimes absent, replaced by a halocline, which is a layer of maximum vertical salinity gradient.

Thermohaline circulation (THC) - Large-scale circulation in the ocean that transforms low-density upper ocean waters to higher-density intermediate and deep waters and returns those waters back to the upper ocean. The circulation is asymmetric, with conversion to dense waters in restricted regions at high latitudes and the return to the surface involving slow upwelling and diffusive processes over much larger geographic regions. The THC is driven by high densities at or near the surface, caused by cold temperatures and/or high salinities, but despite its suggestive though common name, is also driven by mechanical forces such as wind and tides. Frequently, the name THC has been used synonymously with Meridional Overturning Circulation.

Thermokarst - The process by which characteristic landforms result from the thawing of ice-rich permafrost or the melting of massive ground ice.

Threshold - The level of magnitude of a system process at which sudden or rapid change occurs. A point or level at which new properties emerge in an ecological, economic or other system, invalidating predictions based on mathematical relationships that apply at lower levels.

Tide gauge - A device at a coastal location (and some deep-sea locations) that continuously measures the level of the sea with respect to the adjacent land. Time averaging of the sea level so recorded gives the observed secular changes of the relative sea level.

Total solar irradiance - The amount of solar radiation received outside the Earth's atmosphere on a surface normal to the incident radiation, and at the Earth's mean distance from the Sun.

Transpiration - The evaporation of water vapor from the surfaces of leaves through stomata.

Tree line - The upper limit of tree growth in mountains or high latitudes. It is more elevated or more poleward than the forest line.

Tree rings - Concentric rings of secondary wood evident in a cross-section of the stem of a woody plant. The difference between the dense, small-celled late wood of one season and the wide-celled early wood of the following spring enables the age of a tree to be estimated, and the ring widths or density can be related to climate parameters such as temperature and precipitation. See Proxy.

Trophic level - The position that an organism occupies in a food chain.

Trophic relationship - The ecological relationship which results when one species feeds on another.

Troposphere - The lowest part of the atmosphere, from the surface to about 10 kilometers (~6 miles) in altitude at mid-latitudes (ranging from 9 kilometers (~5.6 miles) at high latitudes to 16 kilometers (~10 miles in the tropics on average), where clouds and weather phenomena occur. In the troposphere, temperatures generally decrease with height.

Tsunami - A large wave produced by a submarine earthquake, landslide or volcanic eruption.

Tundra - A treeless, level, or gently undulating plain characteristic of the Arctic and sub-Arctic regions characterized by low temperatures and short growing seasons.

References

Glossaries of the contributions of Working Groups I, II and III to the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report 2007.